1. Field of the Invention
The present invention relates to a wireless communication terminal for performing the establishment of a communication link, a method therefor, a program for executing the method, and a recording medium containing the program. More particularly, the present invention relates to a wireless communication terminal which supports both synchronous communications and asynchronous communications, and is capable of concurrently establishing a plurality of communication links with a plurality of other wireless communication terminals, a method for establishing such communication links, a program for executing the method, and a recording medium having the program recorded thereon.
2. Description of the Related Art
As is well known, communication terminals, e.g., PDA (Personal Digital Assistants), cellular phones, or personal computers, can realize various functions such as an internet connection, LAN (Local Area Network) access, exchange of business card data, telephone calling, music reproduction, and the like. These functions are realized through either asynchronous (ASYNC) communications (which are chiefly used for data transmissions which do not require real time capabilities), or synchronous (SYNC) communications (which are chiefly used for data transmissions which require real time capabilities). Generally speaking, internet connection, LAN access (data communications, file transmission), and exchange of business card data (file transfer) are realized through asynchronous communications. On the other hand, telephone calling (audio communications) and music reproduction (audio communications) are generally realized through synchronous communications.
In recent years, communication terminals are being used in more and more diversified manners. In one manner, a plurality of functions may be simultaneously executed. Examples of functions that can be simultaneously executed are: functions using the same communication mode, such as performing an exchange of business card data during an internet connection (both of which are asynchronous communications), or making telephone calls while listening to music (both of which are synchronous communications); and functions using different communication modes, such as making telephone calls during LAN access (i.e., an asynchronous communication and a synchronous communication).
In the field of wired communications, the IEEE1394 standard or the like already enables communications which involve such simultaneous use of a plurality of functions, i.e., communications involving both asynchronous communications and synchronous communications. In the field of wireless communications, a technique supporting both asynchronous communications and synchronous communications already exists. However, this technique only enables execution of either asynchronous communications or synchronous communications (referred to as “single link communications”), rather than enabling simultaneous execution of asynchronous communications and synchronous communications (referred to as “multi link communications”). Therefore, efforts have been made to develop techniques for realizing simultaneous execution of asynchronous communications and synchronous communications in the field of wireless communications. One example of such a technique is the Bluetooth™ communication standard. For details of Bluetooth communications, see Kazuhiro Miyatsu, “Technology Kaitaishinsho Bluetooth Gijutsu Guide”, 1st ed., Ric Telecom, Ltd., Jun. 11, 2001.
Hereinafter, a technique for simultaneously executing asynchronous communications and synchronous communications will be described with respect to a control module for Bluetooth communications. FIG. 14 is a block diagram illustrating a schematic structure of a conventional wireless communication terminal incorporating a control module for Bluetooth communications.
In FIG. 14, the conventional wireless communication terminal comprises a user input section 110, a link management section 120, communication processing section 130, wireless communication section 140, specific function processing section 150, and a display section 160. The link management section 120 includes an asynchronous communication link management section 121, a synchronous communication link management section 122, an asynchronous communication link control section 123, and a synchronous communication link control section 124.
The user input section 110 receives, from a user, an instruction concerning functions of the wireless communication terminal (begin data transfer, begin download, establish a communication link, etc.), and issues, to the link management section 120, an instruction to establish a communication link, and issues other instructions to the specific function processing section 150.
Hereinafter, the largest number of synchronous (or asynchronous) communication links which can be simultaneously established with other wireless communication terminals will be referred to as the “limit number concerning synchronous (or asynchronous) communication links”. Moreover, the number of synchronous (or asynchronous) communication links which have already been established with other wireless communication terminals will be referred to as the “established number concerning synchronous (or asynchronous) communication links”.
The asynchronous communication link management section 121 retains a limit number and an establish number concerning asynchronous communication links, and based on these numbers, determines whether it is possible to establish an asynchronous communication link which has been designated by the user. The synchronous communication link management section 122 retains a limit number and an established number concerning synchronous communication links, and based on these numbers, determines whether it is possible to establish a synchronous communication link which has been designated by the user. Upon receiving an instruction to establish an asynchronous communication link from the asynchronous communication link management section 121, the asynchronous communication link control section 123 establishes an asynchronous communication link with a corresponding wireless communication terminal by means of the communication processing section 130 and the wireless communication section 140. Upon receiving an instruction to establish a synchronous communication link from the synchronous communication link management section 122, the synchronous communication link control section 124 establishes a synchronous communication link with a corresponding wireless communication terminal by means of the communication processing section 130 and the wireless communication section 140.
The communication processing section 130 performs a process of establishing a communication link and a process instructed by the specific function processing section 150. The wireless communication section 140 carries out a wireless communication with another wireless communication terminal. The specific function processing section 150 is a section which processes functions that are specific to the wireless communication terminal. The display section 160 displays various information related to the wireless communication terminal.
Based on the above structure, the conventional wireless communication terminal realizes not only simultaneous establishment of a plurality of asynchronous communication links or simultaneous establishment of a plurality of synchronous communication links, but also realizes simultaneous establishment of an asynchronous communication link and a synchronous communication link.
An example of a conventional technique related to concurrent establishment of asynchronous communication links is disclosed in the specification of, e.g., Japanese Patent No. 2500097, which relates to adding an asynchronous communication link in a packet communication network. According to this conventional technique, the resource for establishing an asynchronous communication link (average bit rate, deviation of average bit rate, and bandwidth) is checked with respect to each exchange node. If an exchange node has sufficient resource, establishment of an asynchronous communication link is permitted, and if an exchange node does not have sufficient resource, establishment of an asynchronous communication is denied.
The conventional wireless communication terminal having the aforementioned structure carries out the asynchronous communication link management and the synchronous communication link management in independent manners, i.e., without giving consideration to how each other link is established. Therefore, if a request for establishing a synchronous communication link is made when an asynchronous communication link is already established, the conventional wireless communication terminal will establish a synchronous communication link without determining how an asynchronous communication is established (FIG. 15). Since synchronous communications are generally given precedence over asynchronous communications, a problem may occur in the communications in that an already-established asynchronous communication link may be disrupted depending on the communication band (i.e., required communication quality) to be exclusively used by the synchronous communication link which is being established. Note that this problem is unique to wireless communications, where there are limitations on the communication band, and does not pertain to wired communications, which require no particular considerations with respect to the communication band.
The aforementioned problem in wireless communications are illustrated below. FIGS. 16A and 16B are diagrams illustrating an exemplary configuration in which a wireless communication terminal A which functions as a master connected to a public network (a personal computer) establishes a communication link with slave wireless communication terminals B, C, D, and E (cellular phones) FIGS. 17 and 18 are charts illustrating how communication links are established based on a packet type of a different communication quality.
In FIG. 16A, the master wireless communication terminal A has previously established asynchronous communication links with the slave wireless communication terminals B to E for realizing LAN access. In this state, let us assume that the slave wireless communication terminal B newly establishes a synchronous communication link with the master wireless communication terminal A for placing a telephone call via the public network. In this case, the master wireless communication terminal A has not established a synchronous communication link with any of the slave wireless communication terminals B to E, and therefore unconditionally establishes a synchronous communication link with the slave wireless communication terminal B. In general wireless communications, a request for establishing a synchronous communication link contains an instruction concerning the communication band, i.e., communication quality. Therefore, there if no problem if the communication band for the requested synchronous communication link can be secured within a communication band which was unused before the establishment of the synchronous communication link. However, if the communication band for the requested synchronous communication link cannot be secured within the unused communication band, the communication band for the already-established asynchronous communication link is depleted, so that the asynchronous communication link is disrupted (FIG. 16B).
For example, packet types corresponding to communication quality are defined in Bluetooth communications (see pp. 104 and 105 of Bluetooth technology guidelines). An HV1 packet is a packet for a synchronous communication which exclusively uses all of the communication band. An HV2 packet is a packet for a synchronous communication which exclusively uses ½ of the communication band. An HV3 packet is a packet for a synchronous communication which exclusively uses ⅓ of the communication band. A DM1 packet is a packet for a synchronous communications. A DV packet is a packet which, for a synchronous communication link and an asynchronous communication link that are performed between the same pair of wireless communication terminals, can contain both the data of synchronous communication packets (HV1 to HV3) and the data of asynchronous communication packets (DM1) (see p. 106 of the aforementioned Bluetooth guidelines). In Bluetooth communications, there is also a stipulation that a synchronous communication link (HV1 to HV3) can be established after an asynchronous communication link (DM1) is established. Therefore, in the case illustrated in FIG. 16A, there is no problem if a synchronous communication link is requested based on HV2 packets (FIG. 17). On the other hand, if a synchronous communication link is requested based on HV1 packets, there is a problem in that the asynchronous communication links with the slave wireless communication terminals C to E will have to be disrupted (FIG. 18).
Thus, an object of the present invention is to provide a wireless communication terminal which can control the establishment of new synchronous communication links while maintaining already-established a synchronous communication links, a communication link establishment method to be executed by the wireless communication terminal, a program for executing the method, and a recording medium containing the program.